This invention relates generally to optical information storage media, and, more particularly, to optical information storage media, such as cards, having increased storage capacity.
In the information society of today, need exists for storing and, of course, retrieving information in a manner which provides rapidity, low cost, reliability and which is condensed for economy of storage. It is expected that this need will be, in part, met by information storage cards such as bank, medical record, and the like which will have high-capacity data storage features and can, for example, be carried in a wallet.
With the relatively recent progress in optical recording techniques, for example, optically encoded and/or encodable media are preferred in many situations because they can store significantly higher amounts of information than, for example, correspondingly sized magnetic media. There are, however, accepted length, width and thickness standards for such cards. It therefore becomes desirable to increase the information storage capacity of such cards in a manner which does not increase its physical dimensions beyond such standards.
A wide variety of optical data cards already exist. One known type of card has information stored on laser recording media in the form of a stripe. Essentially, the information to be stored is converted to digital code and optically written as a series of micron-size spots or pits and spaces. These pits and spaces are recorded in generally linear tracks. A reader and/or writer device for use therewith must, therefore, perform rectilinear scanning movement with respect to these data tracks. While such an optical card reader and/or writer device uses space on the card satisfactorily, it nonetheless tends to be relatively complicated in construction and operation if high spot density is desirable. Also it is relatively costly to produce. However, in order to use less costly reading and/or writing hardware with such cards, then a compromise with respect to storage capacity is required since larger spot sizes are needed. A low capacity card of this type is described in U.S. Pat. No. 4,500,777.
Another kind of optical record card is described in U.S. Pat. No. 3,501,586, wherein data is recorded onto data tracks which are segmented into arc like raster lines across the surface of the card. Such cards may be read by a playback system, such as illustrated in U.S. Pat. No. 4,090,031, wherein the card is held stationary and each track segment can be read by a corresponding set of scanning elements. While such an optical card and associated hardware serve satisfactorily, they nonetheless tend to have some shortcomings. For instance, the arcuate tracks on the card are interrupted at the card edges. Thus, either the hardware becomes complex by requiring multiple objectives or the data stream is interrupted. Also, tracking and focusing are also relatively more complex than with rectilinear scanning. Significantly, the card surface area of this type card is less well utilized than with the above noted cards using a rectilinear approach because the bow shaped space the data occupies wastes areas at each end of the card.
Still another known approach to putting information on a card is one which has an annular track portion that can be read and/or written on while the card or writing head is rotated about a rotational axis of the card. Examples of this type of card are disclosed in U.S. Pat. No. 3,787,636 and Japanese Patent No. 61-190721. The latter patent describes an optical card utilizing an annular area of an optical recording medium. This card tends, however, not to be as efficient in utilizing card space since it is limited by a single annular band. Even in the situation where the end areas of the card are utilized by arcuate or curvilinear segments outside the noted annular band, such arcuate segments present signficiant focusing and tracking problems insofar as an optical head has to go off the card to read corresponding tracks at both ends of the card. In addition, the hub area cannot be utilized effectively without excessive rotational speed.
The noted disadvantages and shortcomings of the prior art optical storage cards are reduced substantially by reason of the present invention.